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finite-difference time-domain scheme for nonlinear acoustic waves in solids

MECHANICAL SYSTEMS AND SIGNAL PROCESSING 2019年 130卷 790-799页

作者： Wang, Xiaoyu Gong, Xun Qin, Chuanxi Zhang, De Wu, Haodong Zhang, Dong Nanjing Univ Key Lab Modern Acoust Dept Acoust Sci & Enginee Coll PhysMinist EducInst Acoust 22 Hankou Rd Nanjing 210093 Jiangsu Peoples R China

A general finite-difference time-domain (FDTD) method for numerical simulation of the nonlinear acoustic wave in conservative (nondissipative) solids is presented. We apply the spatial derivatives of displacements instead of stress and particle velocity as the bases to discretize the governing partial differential equations. The mathematical model is completely compatible with its linear counterpart. The model solution keeps stable even very near to the formation of a shock wave. As numerical examples, the FDTD scheme is used to investigate the longitudinal and transverse plane waves in infinite isotropic material. In the case of longitudinal wave, a sinusoidal wave transforms into a wave with a sawtooth profile eventually. The distance for the formation of a discontinuity can be obtained directly. The primary and the high order harmonic waves vary with the travelling distance in a very complex way. In the case of transverse wave, high order transverse waves are neglectable and high order longitudinal waves are generated instead. This method dose not need linearization of the governing equations. It can also be used to deal with nonlinear acoustic wave in anisotropic solids without modification. (C) 2018 Elsevier Ltd. All rights reserved.

关键词： Nonlinear acoustic waves in solids finite-difference time-domain method Perturbation theory

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Optical Performance of CMOS Image Sensor Pixels: Simulation Study

Optical Performance of CMOS Image Sensor Pixels: Simulation ...

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International Symposium of the Applied-Computational-Electromagnetics-Society (ACES)

作者： Banejiee, Saswatee Sawai, Yusuke Chen, Anny Miyauchi, Ken Han, Sangman BRILLNICS Japan Inc Tokyo Japan

ISBN: (纸本)9781733509626

CMOS image sensor (CIS) pixels are formed by stacking multiple layers of semiconductor materials. Currently, industrial development of such photonic devices includes a design step where light propagation is simulated using numerical methods such as, finite-difference time-domain (FDTD). We discuss the FDTD simulation of CIS pixels to predict the optical properties as function of wavelength and incident angle.

关键词： CMOS Image Sensors silicon photonics subwavelength optics design and simulation finite-difference time-domain method refractive indices of materials thin films

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Realization of topological superlattices and the associated interface states in one-dimensional plasmonic crystals

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Physical Review B 2022年第4期106卷 045401-045401页

作者： C. Liu H. C. Ong Department of Physics The Chinese University of Hong Kong Shatin Hong Kong

In analogy to the Su-Schrieffer-Heeger (SSH) model, one-dimensional (1D) electromagnetic (EM) crystals can exhibit nontrivial topological properties. When a nontrivial EM crystal is in contact with its trivial counterpart, a topologically protected interface state is formed. While much attention has been focused on a single interface state, multiple interface states can interact collectively when suitable conditions are met, giving rise to nontrivial band topologies resembling the standard SSH model. Here, we study the topological properties of 1D metallic superlattices that support multiple interface states. We first demonstrate that a single interface state exists at the boundary between two topologically distinct metallic arrays that carry Bloch-like surface plasmon polaritons. Such an interface state is then used as the building block for further constructing the superlattices. By exploiting the separation between two dimerized interface states and the distinct inter- and intrainterface configurations to facilitate different intracell and intercell interactions, we vary the band topology of the superlattices. More importantly, a new superlattice interface state is formed when trivial and nontrivial superlattices are brought together. The superlattice interface state is found to have smaller angular divergence and longer localization length than its single counterpart, thus is desired for robust signal transmission and a high finesse cavity.

关键词： Plasmonics Topological effects in photonic systems Superlattices finite-difference time-domain method Reflectivity

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Formulation of the finite-difference time-domain method for the analysis of axially symmetric metal nanodevices

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JOURNAL OF MODERN OPTICS 2012年第16期59卷 1439-1447页

作者： Liu, Yuling Yu, Weixing Zhejiang Univ Technol Coll Sci Hangzhou 310014 Zhejiang Peoples R China Chinese Acad Sci Changchun Inst Opt Fine Mech & Phys State Key Lab Appl Opt Changchun 130033 Peoples R China

A systematic finite-difference time-domain method, established in the cylindrical coordinate and integrated with the six-pole Lorentz-Drude model using the auxiliary differential equation method, is formulated. The model is appropriate for analyzing metal photonic devices with an axially symmetric nanostructure, such as metal nanowires, metal particles, and plasmonic lenses. As an example, an experimentally demonstrated plasmonic lens is analyzed based on the Drude model, the Lorentz-Drude model, and the Lorentz model. Depending on the different dispersion models, distinct electric field distributions for the plasmonic lens are obtained. The interesting numerical results, which are explained in this paper, show the high efficiency and accuracy of the simulation model.

关键词： finite-difference time-domain method plasmonic lens metal nanodevice axially symmetric nanostructure Lorentz-Drude model

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Surface-Emitting Broadband THz Quantum Cascade Laser Frequency Combs with Inverse-Designed Waveguide Facets

Surface-Emitting Broadband THz Quantum Cascade Laser Frequen...

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Conference on Lasers and Electro-Optics Europe (CLEO EUROPE)

作者： Sebastian Gloor Urban Senica Paolo Micheletti Mattias Beck Jérôme Faist Giacomo Scalari Institute of Quantum Electronics ETH Zürich Zürich Switzerland

ISBN: (纸本)9798350345995

THz Quantum Cascade Lasers are unipolar electrically driven semiconductor lasers that can also operate as frequency combs for broadband metrology and sensing [1], [2]. THz quantum cascade lasers are usually processed in double metal waveguide ridges exhibiting low slope efficiencies and a patterned far field [3]. Surrounding the ridge structure with the low-loss polymer Benzocyclobuten (BCB) allows for an extended top contact improving waveguide and thermal properties as well as permitting the implementation of passive structures [4].

关键词： finite-difference time-domain method Frequency combs Laser coupling Laser operation Lasers Semiconductor lasers

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Modelling and analysis of fibre microlenses with ray-tracing and finite-difference methods

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OPTO-ELECTRONICS REVIEW 2022年第1期30卷

作者： Sliwak, Adam Jelen, Mateusz Patela, Sergiusz Wroclaw Univ Sci & Technol Fac Microsyst Ul Janiszeskiego 11-17 PL-50372 Wroclaw Poland

Fibre optic microlenses are small optical elements formed on the end-faces of optical fibres. Their dimensions range from a few tens to hundreds of micrometres. In the article, four optical fibre microlenses are modelled and analysed. Microlenses are used for light beam manipulation and quantitative metrics are needed to evaluate the results, for example, the size of focusing spot or intensity distribution. All four lenses tested are made of rods of the same refractive index;they were welded to a single-mode fibre. Two modelling methods were used to analyse the lenses: ray-tracing and finite-difference time-domain. The ray-tracing algorithm moves rays from one plane to another and refracts them on the surfaces. finite-difference time-domain consists of calculating Maxwell's equations by replacing spatial and temporal derivatives by quotients of finite differences. In this paper, the results of the microlenses analyses obtained from ray-tracing and finite-difference time-domain methods were compared. Both methods of analysis showed the presence of undesirable side lobes related to lens design, namely rods too long for lens fabrication. The test results were compared with the measurements made with the knife-edge method. The use of a single tool to determine parameters of an optical fibre lens does not allow for precise determination of its properties. It is necessary to use different tools and programs. This allows a complete analysis of the beam parameters, letting us find the causes of technical issues that limit the performance of the lenses.

关键词： finite-difference time-domain method knife-edge method microlens ray-tracing

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Nonisothermal cellular automata simulation of two-dimensional snow crystal growth

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Physical Review E 2022年第5期106卷 055309-055309页

作者： X. Y. Xu W. Wang Shanghai Jiao Tong University 800 Dong Chuan Rd. Shanghai 200240 China

Natural snowflakes exhibit remarkable diversity with a fascinating sixfold symmetry and fractal structure. Efforts to discover the snow crystal growth pattern and mechanism behind it have been made in the past 50 years. Among those, cellular automata (CA) have made certain progress. To investigate the influence of latent heat release in snow crystal growth and have a deeper understanding of crystal growth characteristics, an improved CA model combined with vapor diffusion and heat diffusion is proposed to investigate the snowflake growth process in a two-dimensional and nonisothermal field in this paper. Simulation results show that obtained snow crystal growth behavior is consistent with previous experimental observations and satisfies the crystal growth dynamic theory. Latent heat release impacts the small structure of snow crystals, and it could have a more significant influence on snowflake morphology when vapor diffusion is slow and heat diffusion is dominating.

关键词： Crystal growth Cellular automata finite-difference time-domain method Numerical techniques

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Predicting the Q factor and modal volume of photonic crystal nanocavities via deep learning 7

Predicting the <i>Q</i> factor and modal volume of photonic ...

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Conference on Nanophotonics and Micro/Nano Optics VII

作者： Li, Renjie Gu, Xiaozhe Li, Ke Li, Zhen Zhang, Zhaoyu Chinese Univ Hong Kong Sch Sci & Engn SSE Shenzhen Peoples R China Chinese Univ Hong Kong Shenzhen Key Lab Semicond Lasers Shenzhen Peoples R China

ISBN: (数字)9781510646568

ISBN: (纸本)9781510646568;9781510646551

A Deep Learning (DL) based forward modeling approach has been proposed to accurately characterize the relationship between design parameters and the optical properties of Photonic Crystal (PC) nanocavities. The demonstrated DNN model makes predictions not only for the Q factor but also for the modal volume V for the first time, granting us precise control over both properties in the design process. The experimental results show that the DNN has achieved a state-of-the-art performance in terms of prediction accuracy (up to 99.9999% for Q and 99.9890% for V) and convergence speed (i.e., orders-of-magnitude speedup). The proposed approach overcomes shortcomings of existing methods and paves the way for DL-based on-demand and data-driven optimization of PC nanocavities applicable to the rapid prototyping of nanoscale lasers and integrated photonic devices of high Q and small V.

关键词： finite-difference time-domain method Data modeling Performance modeling Optical properties Photonic crystals Statistical modeling Visualization Artificial neural networks Machine learning

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Plasmonic enhancement of light to improve the parameters of solar cells

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APPLIED NANOSCIENCE 2020年第12期10卷 4759-4766页

作者： Havryliuk, O. O. Evtukh, A. A. Pylypova, O. V. Semchuk, O. Yu. Ivanov, I. I. Zabolotnyi, V. F. Chuiko Inst Surface Chem NAS Ukraine 17 Ganeral Naumova Str UA-03164 Kiev Ukraine Lashkaryov Inst Semicond Phys NAS Ukraine 41 Pr Nauki UA-03028 Kiev Ukraine Taras Shevchenko Natl Univ Kyiv Inst High Technol 60 Volodymyrska Str UA-01033 Kiev Ukraine Vinnytsia Mykhailo Kotsiubynskyi State Pedag Univ 32 Ostrozkoho Str UA-21100 Vinnytsia Ukraine

Surface plasmon resonance (SPR) can be generated in metal nanostructures such as gold, silver, copper and aluminium, which are promising materials in the fields of optoelectronics and plasmonics. The SPR in periodic arrays has aroused great interest because of its uniform optical properties which can be applied in integrated optoelectronics device, including solar cells (SC). The optical spectra of structures with Ag nanoparticles on the surface of Si wafer were calculated. The simulation was carried out using finite-difference time-domain method (FDTD). The FDTD method is a powerful numerical algorithm for the direct solution of Maxwell's equations. As a source of radiation, a plane wave with a range of wavelengths 300-1240 nm is used. The enhancement of solar light absorption of structures with Ag nanoparticles has been demonstrated. The Localized Surface Plasmon Resonance peaks have been obtained in the wavelength range of 830-865 nm that is in good agreement with experimentally revealed one. It was shown that the period of Ag nanoparticles replacement significantly influences on the spectra and LSPR peak position. The measurement of current-voltage characteristics of solar cells with and without Ag nanoparticles demonstrated significant enhancement of short current density in case of AgNPs on SCs surface.

关键词： Optical spectra Solar cells Metal nanoparticles Plasmon Localized surface plasmon resonance finite-difference time-domain method

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Modified Photonic Band Gap Via Thermal Shrinkage of Two-Photon Polymerized Distributed Bragg Reflectors

Modified Photonic Band Gap Via Thermal Shrinkage of Two-Phot...

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Conference on Lasers and Electro-Optics Europe (CLEO EUROPE)

作者： Yu-Shao Chen Mike P. C. Taverne C.-C. Huang Ying-Lung Daniel Ho John G. Rarity Department of Electrical and Electronic Engineering University of Bristol Bristol UK Department of Mathematics Physics & Electrical Engineering Northumbria University Newcastle upon Tyne UK Optoelectronics Research Centre University of Southampton Southampton UK

ISBN: (纸本)9798350345995

One-dimensional (1D) polymer-based photonic crystals (PhCs) in the $1.55\ \mu \mathrm{m}$ wavelength range can be easily created using a two-photon direct laser writing system. To achieve shorter period structures, we report the use of thermal shrinkage [1]–[3] of two-photon polymerized structures at elevated temperatures to eliminate unpolymerized material, leading to the uniform shrinkage of distributed Bragg reflector (DBR) structures [4] by a ratio of 2.5 to 5. Our finite difference time domain (FDTD) simulation and the angle-resolved light scattering characterisation technique using Fourier image spectroscopy (FIS) [5]–[7] show that the photonic bandgap (PBG) of DBRs blue-shift in the visible region (650 nm to 500 nm).

关键词： Blue shift Bragg reflectors finite-difference time-domain method Laser systems Optical imaging Photonic crystals

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